nlbutts/sx127x_tools

Code that runs on a Raspberry Pi and communicates to a RFM9x module.

Overview

This library is meant to control an SX127x radio module from a Raspberry Pi. Specifically it was meant to use the Adafruit RFM9x display Bonnet

But it will work with any SX127x/RFM9x device as long as it is probably connected to the Raspberry Pi

Pin Connections

The following pins are used to control the SX127x/RFM9x device

Header Pin	BCM Pin	Usage	Notes
22	25	RFM Reset	Active low
26	7	RFM CS	Active low
15	22	DIO0
16	23	DIO1
18	24	DIO2
23	11	RFM SCLK
19	10	RFM MOSI
21	9	RFM MISO

Setup

Install the prereqs

sudo apt update
sudo apt install -y cmake libprotobuf-dev gstreamer1.0-plugins-good gstreamer1.0-plugins-bad gstreamer1.0-tools gstreamer1.0-omx gstreamer1.0-plugins-base gstreamer1.0-plugins-base-apps libgstreamer-plugins-base1.0-dev libgstreamer1.0-dev

Build

Copy the files to the Raspberry Pi, then run the following:

cd <git checkout directory>
cmake ..
make -j

It will create a static library for the SX127x code and several apps.

• fsk - program to send/receive random data using FSK
• lora - program to send/receive random data using LORA
• fxfer - program to send/receive a file using FSK

File Transfer Protocol

The file transfer app is pretty simple. The payload is preprended with the 16-bit CCITT CRC, 32-bits of the total bytes to follow, then the payload.

| 32-bit payload size | 16-bit CCITT | Payload |

Everything is stored in bit endian format. For example if the CRC is 0x1234 the first byte transmitted would be 0x12 and the second byte would be 0x34.

We would call this new data structure the txpayload. The txpayload is further split into 250 data bytes and a 16-bit sequence counter. The SX127x payload is then 252 bytes

| Sequence number | TxPayload |

Examples

These settings work pretty well for the file transfer: Transmitter

/fxfer -f test.bin --datarate 200000 --dev 110000 -p 5 --crc

Receiver

./fxfer -f test.bin --datarate 200000 --bw 180000 -r --crc

If you add some error correcting codes, then you can remove the CRC and fix bit errors.

Adafruit Bonnect Pinout Reference

This is just for reference, as I got tired looking for the schematic

Header Pin	BCM Pin	Usage	Notes
1		+3.3V
2		+5V
3	2	SDA	Connects to the display
4		+5V
5	3	SCL	Connects to the display
6		GND
7	4	GPIO
8	14	TXD
9		GND
10	15	RXD
11	17	GPIO
12	18	GPIO
13	27	GPIO
15	22	GPIO
16	23	DIO1
17		+3.3V
18	24	DIO2
19	10	RFM MOSI
20		GND
21	9	RFM MISO
22	25	RFM RST	Active Low
23	11	RFM SCLK	Active Low
24	8	CS0
25		GND
26	7	RFM CS	CS1
27	0	EE DATA
28	1	EE CLK
29	5	GPIO	Button
30		GND
31	6	GPIO	Button
32	12	GPIO	Button
33	13	GPIO
34		GND
35	19	GPIO
36	16	GPIO
37	26	GPIO
38	20	GPIO
39		GND
40	21	GND